Studies examining the nature of the SH-Mediated metal binding sites of the 45,000 dalton scallop kidney CdBP in relation to secondary structure are in progress. These data taken in concert with ongoing amino acid sequence and structural studies of oyster CdBP suggest that one evolutionary pathway for MT may involve the insertion of cysteine based sequences into a more ordered protein with concomitant changes in structure and metal-binding site formation or gene cleavage with production of a smaller more efficient molecule from a larger protein. In addition, studies focused on examining the role(s) of this protein in toxicity from multi-element exposure showed that its apparent induction by cadmium exposure ameliorated copper toxicity to the scallops but that this protective effect was associated with marked alterations of normal cytosolic metal-binding patterns for copper, zinc and cadmium.